Airplains 180 HP, CHTs, and leaning

[4RNB]

C172M with new engine, likely approaching 50 hours on it and not needing much oil (1 quart). Perhaps I can stop running the engine hard? Before engine monitor and new engine, my leaning process was to set RPM as desired, then pull mixture back until engine runs a little rough or I see RPM drop, then twist the mixture 2-3 times. When I do this with current set up I see GPM <8 but CHTs go above 400, not 420 though, and EGTs get higher. Yellow warning for CHTs programmed at 400, lycoming redline is 500. Mike Busch would suggest >400 is tough on cylinder longevity and EGTs can be taken more lightly. I end up having to enrich the mixture back near 10 GPM to get CHTs back below 400.

So, If you fly an Airplains 180 HP with engine monitoring, I'd love to hear your figures and processes.

It looks like Airplains says 9.4GPM, see image.

Of note, I still need to get my Airbox baffle installed, hoping this will improve cooling. https://www.pilotsofamerica.com/community/threads/engine-air-intake.142634/#post-3424311

Thanks for any contribution

 

[Jeff767]

it’s to bad you did not install a engine monitor during the swap. It would tell you much more. Is the CHT you mention off one cylinder only and if so which one. If you are seeing 420 at cruise what were you seeing in climb?
I would not fly the aircraft again until you get the air box Baffle installed. Without it you have no idea what is going on with airflow under the cowl and what temp your hottest cylinder might actually be.

 

[4RNB]

it’s to bad you did not install a engine monitor during the swap. It would tell you much more. Is the CHT you mention off one cylinder only and if so which one. If you are seeing 420 at cruise what were you seeing in climb?
I would not fly the aircraft again until you get the air box Baffle installed. Without it you have no idea what is going on with airflow under the cowl and what temp your hottest cylinder might actually be.

I can fly now and keep it cool. I do have a 4 cyl engine monitor. I was not seeing as high as 420, just close to it. I've started changing my post departure climb rate to faster airspeed and around 500 fpm.

 

[AlleyCat67]

I fly a Tiger, and have some of the same issues. In cruise, using POH values for 65-75% power, my CHTs are often at 415F; in climb I get up to 430F. Meanwhile my primary oil temperature gauge sits there happily the low green arc. I've had the baffles inspected and a fin installed for improved airflow, but nothing has really changed much.

FWIW, take a look at Gary Vogt's web page (https://www.aucountry.com/, under Technical Stuff) where he performed a head-to-head comparison of JPI vs. EI engine monitors, and found JPI reads 30-60F hotter than EI. I've reluctantly come to the conclusion that my higher CHT's may well be a JPI monitoring bias. I try to keep the CHT's down in the low 400's, but otherwise I don't angst about it. So far the engine is in excellent shape at 850 TSOH. Will it make it to 2400 hours like last time? We'll see...

 

[Stewartb]

Fuel may be expensive but it’s still cheaper than cylinders!

 

[4RNB]

Fuel may be expensive but it’s still cheaper than cylinders!

AMEN.
I'm not reading of many LOP flyers in this engine.

 

[Stewartb]

What I’d do (based on my engine experience).

1- verify adequate full power fuel flow is at (or preferably higher than) Lycoming specs. An engine that gets hot tends to stay hot. To that, maintain full throttle until you level out.

2- check your average summer day warm cruise leaning authority. In my area I want to have at least 200° difference between full rich and peak EGTs. This is another check for mixture and mixture distribution among four cylinders.

3- verify timing isn’t advanced.

4- verify baffles are good and the top cowl is installed properly to push baffle seals toward engine center. If your baffles were changed they may not have taken a set and that can make top cowl installation tricky. If they’re not correct your top cowl pressure can’t be maintained. If they ARE correct, google cooling lip and ask your mechanic if improving bottom cowl breathing is worth doing.

What’s your static RPM? Your cruise RPM is on the high side. Adding an inch or two of pitch might help you.

 

[4RNB]

What I’d do (based on my engine experience).

1- verify adequate full power fuel flow is at (or preferably higher than) Lycoming specs. An engine that gets hot tends to stay hot. To that, maintain full throttle until you level out. How is this done?

2- check your average summer day warm cruise leaning authority. In my area I want to have at least 200° difference between full rich and peak EGTs. This is another check for mixture and mixture distribution among four cylinders. Can you explain this to me?

3- verify timing isn’t advanced.

4- verify baffles are good and the top cowl is installed properly to push baffle seals toward engine center. If your baffles were changed they may not have taken a set and that can make top cowl installation tricky. If they’re not correct your top cowl pressure can’t be maintained. If they ARE correct, google cooling lip and ask your mechanic if improving bottom cowl breathing is worth doing.

What’s your static RPM? Your cruise RPM is on the high side. Adding an inch or two of pitch might help you. Again, I do not understand what static RPM is. I'm cruising high RPM with new engine. Inch or two of pitch? Prop is fixed.

 

[Stewartb]

1-Many (most) carbs in recent years are set up too lean. You need a fuel flow gauge to know what your full power flow is. If a little on the lean side? The engine will get hot on initial climb-out, then…

2-If you can’t adjust at least 150° between full rich and peak in cruise you don’t have enough fuel flow to control engine temps, especially for cool weather ops where the engine requires more fuel.

An aluminum fixed pitch prop can be re-pitched. If it’s the same prop you had before? Increased power needs more pitch. Static RPM is listed in the TCDS or STC and is a condition of airworthiness. When I had fixed pitch I wanted 2400 RPM static for STOL performance. Cruise props would have lower static RPM than that.

 

[1RTK1]

I fly a Tiger, and have some of the same issues. In cruise, using POH values for 65-75% power, my CHTs are often at 415F; in climb I get up to 430F. Meanwhile my primary oil temperature gauge sits there happily the low green arc. I've had the baffles inspected and a fin installed for improved airflow, but nothing has really changed much.

FWIW, take a look at Gary Vogt's web page (https://www.aucountry.com/, under Technical Stuff) where he performed a head-to-head comparison of JPI vs. EI engine monitors, and found JPI reads 30-60F hotter than EI. I've reluctantly come to the conclusion that my higher CHT's may well be a JPI monitoring bias. I try to keep the CHT's down in the low 400's, but otherwise I don't angst about it. So far the engine is in excellent shape at 850 TSOH. Will it make it to 2400 hours like last time? We'll see...

Alleycat, I don’t have any problem keeping my tiger well below 400*. Recently I bought the nose gear boot replacement from Gary, it from what I can tell so fa, knocked 20+ degrees off of CHT. Havent flown on a real hot day yet

 

[4RNB]

1-Many (most) carbs in recent years are set up too lean. You need a fuel flow gauge to know what your full power flow is. If a little on the lean side? The engine will get hot on initial climb-out, then…

2-If you can’t adjust at least 150° between full rich and peak in cruise you don’t have enough fuel flow to control engine temps, especially for cool weather ops where the engine requires more fuel.

An aluminum fixed pitch prop can be re-pitched. If it’s the same prop you had before? Increased power needs more pitch. Static RPM is listed in the TCDS or STC and is a condition of airworthiness. When I had fixed pitch I wanted 2400 RPM static for STOL performance. Cruise props would have lower static RPM than that.

I have an engine monitor that shows fuel flow, I forget climb out specifics, but was surprised how high it got, like 15ish?

OK, I get the pitch now. Senseninich 76EM8S14 has a range of 56-62. Not clearly spelled out in log but has a 0-60 listed after that part number. My assumption is this is 60 degree pitch.

 

[Stewartb]

15 sounds low but I’m not near an engine manual.

 

[idahoflier]

I fly a C-172N Air Plains conversion and had an engine monitor installed at overhaul 3 1/2 years ago. Eye opening. Had I flown without the engine monitor and a stock EGT guage I would have been likely cooking cylinders.

Now I climb full rich regardless of altitude and usually have to perform some sort of stair step if I have to climb more than 5,000 ft in the summer.

One thing that helped a lot was this: https://aircraftspeedmods.ca/products/exhaust-fairing-stc-sta-2/ They claim up to 20° decrease in Cyl Temps. I didn't see that dramatic of a drop, but I did see 10° - 12° which I found worth while, especially when you creep up close to 400°. I have one cylinder (#4 of all) that runs consistently at lease 10° warmer than the next closest cylinder and sometimes 18° warmer. It seems to run the leanest most of the time but I haven't been able to detect and induction leak. If it wasn't for that one cylinder I think the exhaust fairing would have completely cured my CHT issues...

 

[4RNB]

I fly a C-172N Air Plains conversion and had an engine monitor installed at overhaul 3 1/2 years ago. Eye opening. Had I flown without the engine monitor and a stock EGT guage I would have been likely cooking cylinders.

Now I climb full rich regardless of altitude and usually have to perform some sort of stair step if I have to climb more than 5,000 ft in the summer.

One thing that helped a lot was this: https://aircraftspeedmods.ca/products/exhaust-fairing-stc-sta-2/ They claim up to 20° decrease in Cyl Temps. I didn't see that dramatic of a drop, but I did see 10° - 12° which I found worth while, especially when you creep up close to 400°. I have one cylinder (#4 of all) that runs consistently at lease 10° warmer than the next closest cylinder and sometimes 18° warmer. It seems to run the leanest most of the time but I haven't been able to detect and induction leak. If it wasn't for that one cylinder I think the exhaust fairing would have completely cured my CHT issues...

Thanks. I have a Powerflo exhaust and my fairing resembles that.

What CHTs, at what RPM and fuel burn do you observe?
Can you run LOP?

 

[idahoflier]

Thanks. I have a Powerflo exhaust and my fairing resembles that.

What CHTs, at what RPM and fuel burn do you observe?
Can you run LOP?

Unfortunately I don't have good data for you because I didn't opt to install a fuel flow meter. I can give you "on average" numbers. I typically cruise at 2500 -2550 and burn 9 - 9.5 GPH. On hot days if I have to climb high I can see fuel consumption go up to 10 - 10.5 GPH because of the rich mixture climbs. I don't run LOP as I my EGT's are to far apart...

 

[Pilawt]

I fly a C-172N Air Plains conversion and had an engine monitor installed at overhaul 3 1/2 years ago. Eye opening. Had I flown without the engine monitor and a stock EGT guage I would have been likely cooking cylinders.

Now I climb full rich regardless of altitude and usually have to perform some sort of stair step if I have to climb more than 5,000 ft in the summer.

One thing that helped a lot was this: https://aircraftspeedmods.ca/products/exhaust-fairing-stc-sta-2/ They claim up to 20° decrease in Cyl Temps. I didn't see that dramatic of a drop, but I did see 10° - 12° which I found worth while, especially when you creep up close to 400°. I have one cylinder (#4 of all) that runs consistently at lease 10° warmer than the next closest cylinder and sometimes 18° warmer. It seems to run the leanest most of the time but I haven't been able to detect and induction leak. If it wasn't for that one cylinder I think the exhaust fairing would have completely cured my CHT issues...

Yep. My 172N (Air Plains 180 hp, long-stack Power-Flow) had one of those Maple Leaf fairings, and it did a good job keeping CHT down.

One of the 180 hp conversion's biggest advantages is the ability to cruise-climb > 100 KIAS. Even here in AZ that kept CHTs at or below 400°.

 

[idahoflier]

Yep. My 172N (Air Plains 180 hp, long-stack Power-Flow) had one of those Maple Leaf fairings, and it did a good job keeping CHT down.

One of the 180 hp conversion's biggest advantages is the ability to cruise-climb > 100 KIAS. Even here in AZ that kept CHTs at or below 400°.

I think I looked into it at your recommendation. Thanks again!

 

[Jeff767]

15 sounds low but I’m not near an engine manual.

9 to 10% of rated HP is ballpark.